Vacuum may be generated in an engine to create various actions that aid in operation of a vehicle. In one example, vacuum may be utilized to provide an actuating force for a device, such as for brake assist. In another example, vacuum may be utilized to circulate various fluids such as for exhaust gas recirculation (EGR), fuel vapor purge, crankcase venting, etc.
In one example, a vehicle includes an engine having a throttle valve that is positioned upstream of a compressor inlet of a turbocharger. The throttle valve is operable to throttle fluid (e.g., intake air) entering the compressor inlet to generate vacuum. Such vacuum may be directed to operate an actuator or circulate other fluids during engine operation.
However, the inventors herein have recognized potential issues with such an approach. The typical pre-compressor throttle can either control engine load or control pre-compressor vacuum but it cannot do both with complete independence. For example, throttling the compressor inlet of the turbocharger reduces flow circulation through the compressor that may result in a choke or stall. Moreover, transient flow conditions created by adjustment of the throttle valve may cause compressor surge. In either case, when such a condition occurs, drivability of the vehicle may be reduced and may be negatively perceived by a vehicle operator.
Thus, in one example, some of the above issues may be addressed by a method for supplying vacuum in an engine. The method includes controlling a throttle valve positioned upstream of a supercharger arranged in series with and upstream of a turbocharger to draw a fluid from a vacuum line positioned intermediate the throttle valve and a supercharger inlet.
By throttling the supercharger, vacuum may be generated for various uses throughout engine operation without restricting flow of the turbocharger. In this way, compressor stall/surge of the turbocharger may be reduced or eliminated.
Furthermore, in some implementations, the supercharger may be utilized to compensate for turbocharger lag. In particular, the supercharger may be operated to provide compression of intake air while the turbocharger is spinning up to operating speed. In one example, the method may include during a vehicle launch condition, adjusting the throttle valve to increase flow through the supercharger inlet and reduce flow from the vacuum line. In this way, more efficient supercharger operation may be prioritized over vacuum generation in order to speed up vehicle launch.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.